This invention relates generally to digital control apparatus, and more specifically to the design of a digital controller for a multimedia photographic projection system whereby plural projectors can be selectively turned on and off and the projection lamps therein controlled to provide variable dissolve rates, either under manual or automatic control.
In the prior art, there are disclosed a variety of techniques for controlling plural photographic film and slide projectors so as to provide desires visual effects. For example, programmable devices are known whereby the turn-on and turn-off times for the film advance drive of plural motion picture projectors or the slide advance of slide projectors can be controlled without the need for manual intervention. Also, it is known that special visual effects can be achieved by controlling the rate at which the projection lamps of selected ones of plural projectors are brought up to full illumination and subsequently dimmed. However, such prior art devices have tended to be quite complex and somewhat expensive. Also, the limited flexibility of the prior art controllers tends to make it difficult to obtain a wide variety of desired presentations.
The programmable audio-visual display device controller of the present invention obviates all of the foregoing limitations. Because it used digital techniques throughout, and is fabricated from well-known and commercially available digital logic components. Also, the manner in which command words are generated and transmitted to selected projectors while being simultaneously recorded on magnetic tape for later automatic control of such projectors allows the utmost in flexibility of control of the operating parameters of the audio/visual display devices employed in the system. In accordance with the teachings of the present invention, there is provided an operator's console having three banks of manually-operable push-button switches. In the first bank are switches, equal in number to the number of projection devices to be controlled, for selectively controlling the ON/OFF state of the film advance mechanism in the projectors. In the second bank are a number of switches, again equal in number to the number of projection devices to be controlled, for selectively governing the rate at which the projection lamps in the plural projectors are illuminated and dimmed. The third bank of switches includes a Cue Stop switch and a Fast-Forward switch for controlling a cartridge type magnetic tape recorder/reproducer. Each time any one of the switches in the plural banks is operated, a digital code word is generated in a parallel format. The parallel word is serialized and transmitted to a receiver and at the same time the serial version of the command word may be stored on magnetic tape. The transmitted serial version of the command word is sent to a receiver module which reconstructs the command word into the parallel format. Subsequently, the command word is decoded by digital logic circuitry and applied to the appropriate control segments in the projectors. Once a program has been prepared to the satisfaction of the operator, he may place the magnetic tape in a playback mode and transmit the serially recorded code words from the tape to the aforementioned receiver network where the code words are reconstructed in a parallel format for application to the decoder network. Because the tape device employed is of the cartridge variety utilizing an endless loop, it is often the case that the desired program does not completely fill the available space on the tape. The operator may encode a fast-forward command by suitable operating the Fast-Forward switch in the third bank of manually operable push-button switches and when this command is sensed by the decoder network a circuit comes into play to drive the endless loop of magnetic tape at two times its normal speed to bring it to a desired reference point so that the programmed visual display may be repeated.